This application is directed to photovoltaic solar cell construction. In particular, it is directed to a protective layer within a housing of a photovoltaic panel or module that surrounds and/or encapsulates the active photovoltaic device within the housing or module.
FIG. 1 is a schematic block diagram of a conventional photovoltaic device. A photovoltaic module 10 can typically have one or more photovoltaic cells 12a-b disposed within it. A photovoltaic cell conventionally is made by having a semiconductor junction 14 disposed between a layer of conducting material 18 and a layer of transparent conducting material 16. Light impinges upon the photovoltaic module 10 and transmits through the transparent conducting material layer 16. Within the semiconductor junction layer 14, the photons interact with the material to produce electron-hole pairs. The semiconductor(s) typically is/are doped creating an electric field extending from the junction layer 14. Accordingly, when the holes and/or electrons are created by the sunlight in the semiconductor, they will migrate depending on the polarity of the device either to the transparent conducting material layer 16 or the conducting material layer 18. This migration creates current within the cell which is routed out of the cell for storage and/or instantaneous use.
One conducting node of the solar cell 12a is shown electrically coupled to an opposite node of another solar cell 12b. In this manner, the current created in one cell may be transmitted to another, where it is eventually collected. The currently depicted apparatus in FIG. 1 is shown where the solar cells are coupled in series, thus creating a higher voltage device. In another manner, (not shown) the solar cells can be coupled in parallel which increases the resulting current rather than the voltage. In any case, the current application is directed to any solar cell apparatus, whether they are electrically coupled in series, in parallel, or any combination thereof.
FIG. 2 is a schematic block diagram of a photovoltaic apparatus. The photovoltaic apparatus has a photovoltaic panel 20, which contains the active photovoltaic devices, such as those described supra. The photovoltaic panel 20 can be made up of one or multiple photovoltaic cells, photovoltaic modules, or other like photovoltaic devices, singly or multiples, solo or in combination with one another. A frame 22 surrounds the outer edge of the photovoltaic panel that houses the active photovoltaic devices. The frame 22 can be disposed flat or at an angle relative to photovoltaic panel 20.
FIG. 3 is a side cross sectional view of the photovoltaic apparatus shown in FIG. 2. In this case, the cross section is taken along the line A-A′ shown above in FIG. 2. The photovoltaic panel has a photovoltaic solar device 18 disposed within the frame 22. A glass, plastic, or other translucent barrier 26 is held by the frame 22 to shield the photovoltaic device 18 from an external environment. In some conventional photovoltaic apparatuses, another laminate layer 24 is placed between the photovoltaic device 18 and the translucent barrier 26.
Light impinges through the transparent barrier 26 and strikes the photovoltaic device 18. When the light strikes and is absorbed in the photovoltaic device 18, electricity can be generated much like as described with respect to FIG. 1.
While the transparent barrier 26 is designed to shield the photovoltaic device 18 from an external environment, many times the protection afforded by the transparent barrier 26 is insufficient. In many conventional photovoltaic panels, the transparent barrier 26 is wedged to the frame and bordered by a rubber gasket seal. While the protection of such a seal can be sufficient, the rubber seal will erode and/or decompose over time. Accordingly, portions of the external environment can impinge upon the semiconductor portion of the photovoltaic device 18, diminishing its performance. Further, upon the creation the photovoltaic apparatus, moisture and other contaminants that might be present during the manufacturing process might be present within the space within the frame 22. Again, such moisture and/or other contaminants could interfere with an efficient operation of the photovoltaic device 18.
In some conventional applications, a laminate 24 is placed between the photovoltaic device 18 and the transparent barrier 26. This laminate 24 can be heated so that it melts and affixes to the photovoltaic device 18 as well as the transparent barrier 26, providing further environmental protection for the photovoltaic device 18. One such type of laminate used in photovoltaic apparatuses is ethylene vinyl acetate (EVA). The EVA is applied to the active photovoltaic device, heated and then fused to the device and laminate materials under pressure. At a temperature of about 85° C., the EVA melts and flows into the volume about the photovoltaic device, and at approximately 120-125° C., the EVA starts to crosslink.
It should be noted that the above identified melting process requires many more steps to make the full panel. Further, the heating performed on the laminate requires the photovoltaic device to be subjected at least in part to the applied thermal energy. In some cases this can adversely affect the photovoltaic device itself. Furthermore, the laminate such as EVA has the additional drawback that such materials are frangible. Thus, if there is an accident in which the transparent conduction material 16 or 18 shatters, the laminate layer will also shatter. Accordingly, what is needed in the art are improved layers, disposed between the encasing structure and the photovoltaic device that will prevent shattering and that protect the photovoltaic device.